Many cases of sensitive information leakage have occurred by file sharing software such as P2P. Those cases have been caused by such reasons as an insufficient security guard of the personal computer (hereinafter, referred to as PC). For the purpose of preventing recurrence of such sensitive information leakage cases, corporations and public agencies adopt measures below:                A system administrator advances the security guard of a PC owned by each user.        
Install security software such as antivirus software and spyware monitoring software onto a PC and instructs each user to comply with security compliance requirements.
Install a health check utility that monitors whether the PC of each user satisfies the defined security compliance requirements onto each PC.                The system administrator forbids users to use removable media that may be connected to a PC with insufficient security guard such as a portable hard disk, USB memory, card memory and the like. For the purpose of forbidding the users to use the media, the system administrator disables the USB slot at the BIOS level and limits access to the BIOS by using passwords.        The system administrator instructs staff users to encrypt files in order to prevent those other than the staff users from viewing the information.Even with the above-described guard, the PC may be subjected to illegal access when a user forgets to update a definition file of the security software. In addition, the above-described guard requires the user to perform an additional task when the user is to bring out a file or a task of encrypting a file at each time when the user operates the file. That lowers usability of each user, and further degrades the work efficiency of the office work.        